Ohms Law Load Amp Resistance Change

I have a solar cell that is rated 3.6 amps .5 volts 1.8 watts when you take a ammeter it does put out 3.6 amps, but this is basically a dead short reading. What I want to know is these cells put out .5 volts using ohms law how much resistance is needed to have a voltage output of .3 volts so you can then measure how many amps are flowing?

I know you could do this with a pot, ammeter, and voltmeter connected to the solar cell then as you start turning up the resistance the voltage output will drop from .5 volts to .3 volts then you can see how many amps are flowing. but it seems that you should be able to figure this out using ohms law?

This is basically a two step problem first find resistance then amps. What I am working on is a solar panel that has 39 cells and when tested it does put out 3.6 amps and has 24 volts no load and what I want to know if this is connected to a battery and the voltage output drops to 12 volts how many amps are flowing at this point?